Random access channel (rach)-less timing advance determination

ABSTRACT

This disclosure provides systems, methods and apparatus for determining a target base station timing advance value between a user equipment (UE) and target base station in connection with a random access channel (RACH)-less handover procedure. In one aspect, the UE may determine the target base station&#39;s timing advance based at least in part on a timing difference between the target base station and the source base station and based at least in part on a timing offset associated with an uplink and a downlink of the UE. In some aspects, the target base station may determine the timing advance using an uplink reference signal of the UE. In some aspects, the UE may report a timing difference between the target base station and the source base station, and the source cell may determine a timing advance based at least in part on the timing difference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/794,091, filed on Feb. 18, 2020, entitled “RANDOM ACCESS CHANNEL(RACH)-LESS TIMING ADVANCE DETERMINATION” (now U.S. Pat. No.11,082,898), which claims priority to U.S. Provisional PatentApplication No. 62/808,151, filed on Feb. 20, 2019, entitled “RANDOMACCESS CHANNEL (RACH)-LESS TIMING ADVANCE DETERMINATION,” and assignedto the assignee hereof. The disclosures of which are considered part ofand are incorporated by reference in this application.

TECHNICAL FIELD

Aspects of the present disclosure generally relate to wirelesscommunication, and more particularly to techniques and apparatuses for arandom access channel (RACH)-less timing advance determination.

DESCRIPTION OF THE RELATED TECHNOLOGY

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (for example,bandwidth, transmit power, etc.). Examples of such multiple-accesstechnologies include code division multiple access (CDMA) systems, timedivision multiple access (TDMA) systems, frequency-division multipleaccess (FDMA) systems, orthogonal frequency-division multiple access(OFDMA) systems, single-carrier frequency-division multiple access(SC-FDMA) systems, time division synchronous code division multipleaccess (TD-SCDMA) systems, and Long Term Evolution (LTE).LTE/LTE-Advanced is a set of enhancements to the Universal MobileTelecommunications System (UMTS) mobile standard promulgated by theThird Generation Partnership Project (3GPP).

A wireless communication network may include a number of base stations(BSs) that can support communication for a number of user equipment(UEs). A user equipment (UE) may communicate with a base station (BS)via the downlink (DL) and uplink (UL). The DL (or forward link) refersto the communication link from the BS to the UE, and the UL (or reverselink) refers to the communication link from the UE to the BS. As will bedescribed in more detail herein, a BS may be referred to as a NodeB, anLTE evolved nodeB (eNB), a gNB, an access point (AP), a radio head, atransmit receive point (TRP), a New Radio (NR) BS, or a 5G NodeB.

The above multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent user equipment to communicate on a municipal, national,regional, and even global level. NR, which also may be referred to asκG, is a set of enhancements to the LTE mobile standard promulgated bythe Third Generation Partnership Project (3GPP). NR is designed tobetter support mobile broadband Internet access by improving spectralefficiency, lowering costs, improving services, making use of newspectrum, and better integrating with other open standards using OFDMwith a cyclic prefix (CP) (CP-OFDM) on the DL, using CP-OFDM or SC-FDM(for example, also known as discrete Fourier transform spread OFDM(DFT-s-OFDM)) on the UL (or a combination thereof), as well assupporting beamforming, multiple-input multiple-output (MIMO) antennatechnology, and carrier aggregation. However, as the demand for mobilebroadband access continues to increase, there exists a need for furtherimprovements in LTE and NR technologies.

SUMMARY

The systems, methods and devices of this disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein.

One innovative aspect of the subject matter described in this disclosurecan be implemented in a method of wireless communication performed by anapparatus of a user equipment (UE). The method may include receivinginformation identifying a timing offset associated with uplink (UL) anddownlink (DL) communications of the UE. The method may includedetermining a target base station timing advance value for a handover toa target base station based at least in part on at least one of theinformation identifying the timing offset, a timing difference betweenthe target base station and a source base station associated with theUE, or a source base station timing advance value associated with thesource base station.

In some implementations, the timing difference is based at least in parton a reference signal timing difference between the target base stationand the source base station. In some implementations, the method caninclude determining the timing difference between the target basestation and the source base station based at least in part on referencesignaling received from the source base station and the target basestation. In some implementations, the timing offset is based at least inpart on a switching time, a propagation delay between transmit andreception, or a hardware configuration of at least one of the UE, thesource base station, or the target base station.

In some implementations, a granularity of the timing offset is based atleast in part on at least one of a numerology, or a slot length of thetarget base station. In some implementations, the informationidentifying the timing offset is received in a handover command. In someimplementations, the target base station timing advance value isdetermined without performing a random access procedure. In someimplementations, the target base station timing advance value isdetermined based at least in part on the information identifying thetiming offset, the timing difference between the target base station andthe source base station, and the source base station timing advancevalue.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus of a UE for wirelesscommunication. The UE may include memory and one or more processorsoperatively coupled to the memory. The memory and the one or moreprocessors may be configured to receive information identifying a timingoffset associated with UL and DL communications of the UE; and determinea target base station timing advance value for a handover to a targetbase station based at least in part on at least one of the informationidentifying the timing offset, a timing difference between the targetbase station and a source base station associated with the UE, or asource base station timing advance value associated with the source basestation. In some aspects, the UE may perform or implement any one ormore of the aspects described in connection with the method, above orelsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a non-transitory computer-readablemedium. The non-transitory computer-readable medium may store one ormore instructions for wireless communication. The one or moreinstructions, when executed by one or more processors of a UE, may causethe one or more processors to receive information identifying a timingoffset associated with UL and DL communications of the UE; and determinea target base station timing advance value for a handover to a targetbaes station based at least in part on at least one of the informationidentifying the timing offset, a timing difference between the targetbase station and a source base station associated with the UE, or asource base station timing advance value associated with the source basestation. In some aspects, the non-transitory computer-readable mediummay implement any one or more of the aspects described in connectionwith the method, above or elsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus for wirelesscommunication. The apparatus may include means for receiving informationidentifying a timing offset associated with UL and DL communications ofthe apparatus; and means for determining a target base station timingadvance value for a handover to a target base station based at least inpart on at least one of the information identifying the timing offset, atiming difference between the target base station and a source basestation associated with the UE, or a source base station timing advancevalue associated with the source base station. In some aspects, theapparatus may include means for performing or implementing any one ormore of the aspects described in connection with the method, above orelsewhere herein.

One innovative aspect of the subject matter described in this disclosurecan be implemented in a method of wireless communication performed by anapparatus of a UE. The method may include transmitting at least one of:information identifying a timing difference between a target basestation and a source base station associated with a handover, or anuplink reference signal; and receiving information identifying a targetbase station timing advance value, where the information identifying thetarget base station timing advance value is based at least in part onthe timing difference between the target base station and the sourcebase station or the uplink reference signal.

In some implementations, the handover is performed without performing arandom access procedure. In some implementations, the informationidentifying the timing difference between the target base station andthe source base station is a quantization of the timing differencebetween the target base station and the source base station. In someimplementations, the information identifying the timing differencebetween the target base station and the source base station is providedin a radio resource management report. In some implementations, theuplink reference signal includes a sounding reference signal.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus of a UE for wirelesscommunication. The UE may include memory and one or more processorsoperatively coupled to the memory. The memory and the one or moreprocessors may be configured to transmit at least one of: informationidentifying a timing difference between a target base station and asource base station associated with a handover, or an uplink referencesignal; and receive information identifying a target base station timingadvance value, where the information identifying the target base stationtiming advance value is based at least in part on the timing differencebetween the target base station and the source base station or theuplink reference signal. In some aspects, the UE may perform orimplement any one or more of the aspects described in connection withthe method, above or elsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a non-transitory computer-readablemedium. The non-transitory computer-readable medium may store one ormore instructions for wireless communication. The one or moreinstructions, when executed by one or more processors of a UE, may causethe one or more processors to transmit at least one of: informationidentifying a timing difference between a target base station and asource base station associated with a handover, or an uplink referencesignal; and receive information identifying a target base station timingadvance value, where the information identifying the target base stationtiming advance value is based at least in part on the timing differencebetween the target base station and the source base station or theuplink reference signal. In some aspects, the non-transitorycomputer-readable medium may implement any one or more of the aspectsdescribed in connection with the method, above or elsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus for wirelesscommunication. The apparatus may include means for transmitting at leastone of: information identifying a timing difference between a targetbase station and a source base station associated with a handover, or anuplink reference signal; and receiving information identifying a targetbase station timing advance value, where the information identifying thetarget base station timing advance value is based at least in part onthe timing difference between the target base station and the sourcebase station or the uplink reference signal. In some aspects, theapparatus may include means for performing or implementing any one ormore of the aspects described in connection with the method, above orelsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a method of wireless communicationperformed by an apparatus of a target base station. The method mayinclude receiving, from a UE, at least one of: information identifying atiming difference between the apparatus of the target base station and asource base station, where the apparatus of the target base station andthe source base station are associated with a handover of the UE, or anuplink reference signal; and providing, to the UE, informationidentifying a target base station timing advance value, where the targetbase station timing advance value is based at least in part on theinformation identifying the timing difference or the uplink referencesignal.

In some implementations, the information identifying the timingdifference between the apparatus of the target base station and thesource base station is a quantization of the timing difference betweenthe apparatus of the target base station and the source base station. Insome implementations, the information identifying the timing differencebetween the apparatus of the target base station and the source basestation is received in a radio resource management report. In someimplementations, the uplink reference signal includes a soundingreference signal. In some implementations, the method can includedetermining the target base station timing advance value based at leastin part on the information identifying the timing difference between theapparatus of the target base station and the source base station or theuplink reference signal.

In some implementations, the method can include selecting a techniquefor determining the target base station timing advance value based atleast in part on the information identifying the timing differencebetween the apparatus of the target base station and the source basestation or the uplink reference signal. In some implementations, thetechnique is selected from a plurality of techniques including at leastone of: determining the target base station timing advance value aszero, determining the target base station timing advance value inaccordance with a source base station timing advance value associatedwith the source base station, or determining the target base stationtiming advance value using the uplink reference signal.

In some implementations, the method may include providing theinformation identifying the target base station timing advance value tothe source base station to be transmitted to the UE. In someimplementations, the handover is performed without performing a randomaccess procedure.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus of a target base stationfor wireless communication. The BS may include memory and one or moreprocessors operatively coupled to the memory. The memory and the one ormore processors may be configured to receive, from a UE, at least oneof: information identifying a timing difference between the target basestation and a source base station, where the target base station and thesource base station are associated with a handover, or an uplinkreference signal; and provide, to the UE, information identifying atarget base station timing advance value aw the target base station,where the target base station timing advance value is based at least inpart on the information identifying the timing difference or the uplinkreference signal. In some aspects, the target base station may performor implement any one or more of the aspects described in connection withthe method, above or elsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a non-transitory computer-readablemedium. The non-transitory computer-readable medium may store one ormore instructions for wireless communication. The one or moreinstructions, when executed by one or more processors of a target basestation, may cause the one or more processors to receive, from a UE, atleast one of: information identifying a timing difference between thetarget base station and a source base station, where the target basestation and the source base station are associated with a handover, oran uplink reference signal; and provide, to the UE, informationidentifying a target base station timing advance value associated withthe target base station, where the target base station timing advancevalue is based at least in part on the information identifying thetiming difference or the uplink reference signal. In some aspects, thenon-transitory computer-readable medium may implement any one or more ofthe aspects described in connection with the method, above or elsewhereherein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus for wirelesscommunication. The apparatus may include means for receiving, from a UE,at least one of: information identifying a timing difference between theapparatus and a source base station, where the apparatus and the sourcebase station are associated with a handover, or an uplink referencesignal; and means for providing, to the UE, information identifying atarget base station timing advance value associated with the apparatus,where the target base station timing advance value is based at least inpart on the information identifying the timing difference or the uplinkreference signal. In some aspects, the apparatus may include means forperforming or implementing any one or more of the aspects described inconnection with the method, above or elsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a method of wireless communicationperformed by an apparatus of a source base station. The method mayinclude determining a timing offset of a UE, where the timing offset isbased at least in part on a difference between a downlink propagationdelay and an uplink propagation delay of the UE; and transmitting, tothe UE in connection with a handover of the UE from the apparatus of thesource base station to a target base station, information identifyingthe timing offset.

In some implementations, the timing offset is based at least in part ona switching time, a propagation delay between transmit and reception, ora hardware configuration of at least one of the UE, the apparatus of thesource base station, or the target base station. In someimplementations, the information identifying the timing offset istransmitted in connection with a handover command. In someimplementations, a granularity of the timing offset is based at least inpart on a numerology or a slot length of the target base station.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus of a source base stationfor wireless communication. The source base station may include memoryand one or more processors operatively coupled to the memory. The memoryand the one or more processors may be configured to determine a timingoffset of a UE, where the timing offset is based at least in part on adifference between a downlink propagation delay and an uplinkpropagation delay of the UE; and transmit, to the UE in connection witha handover of the UE from the apparatus of the source base station to atarget base station, information identifying the timing offset. In someaspects, the source base station may perform or implement any one ormore of the aspects described in connection with the method, above orelsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a non-transitory computer-readablemedium. The non-transitory computer-readable medium may store one ormore instructions for wireless communication. The one or moreinstructions, when executed by one or more processors of a source basestation, may cause the one or more processors to determine a timingoffset of a UE, where the timing offset is based at least in part on adifference between a downlink propagation delay and an uplinkpropagation delay of the UE; and transmit, to the UE in connection witha handover of the UE from the source base station to a target basestation, information identifying the timing offset. In some aspects, thenon-transitory computer-readable medium may implement any one or more ofthe aspects described in connection with the method, above or elsewhereherein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus for wirelesscommunication. The apparatus may include means for determining a timingoffset of a UE, where the timing offset is based at least in part on adifference between a downlink propagation delay and an uplinkpropagation delay of the UE; and means for transmitting, to the UE inconnection with a handover of the UE from the apparatus to a target basestation, information identifying the timing offset. In some aspects, theapparatus may include means for performing or implementing any one ormore of the aspects described in connection with the method, above orelsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a method of wireless communicationperformed by an apparatus of a source base station. The method mayinclude receiving, from a UE, information identifying a timingdifference between the apparatus of the source base station and a targetbase station of a handover of the UE, wherein the timing differencebetween the apparatus of the source base station and the target basestation is associated with a handover of the UE; and transmittinginformation identifying a target base station timing advance value basedat least in part on the information identifying the timing differencebetween the apparatus of the source base station and the target basestation.

In some implementations, the information identifying the timingdifference between the apparatus of the source base station and thetarget base station is a quantization of the timing difference. In someimplementations, the information identifying the timing differencebetween the apparatus of the source base station and the target basestation is received in a radio resource management report. In someimplementations, the information identifying the target base stationtiming advance value is transmitted in connection with a handovercommand.

In some implementations, the method may include determining the targetbase station timing advance value based at least in part on theinformation identifying the timing difference between the apparatus ofthe source base station and the target base station. In someimplementations, the method may include selecting a technique fordetermining the target base station timing advance value based at leastin part on the information identifying the timing difference between theapparatus of the source base station and the target base station. Insome implementations, the technique is selected from a plurality oftechniques including at least one of determining the target base stationtiming advance value as zero, determining the target base station timingadvance value in accordance with a source base station timing advancevalue associated with the source base station, or determining the targetbase station timing advance value using an uplink reference signal.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus of a source base stationfor wireless communication. The source base station may include memoryand one or more processors operatively coupled to the memory. The memoryand the one or more processors may be configured to receive, from a UE,information identifying a timing difference between the source basestation and a target base station, wherein the timing difference betweenthe apparatus of the source base station and the target base station isassociated with a handover of the UE; and transmit informationidentifying a target base station timing advance value based at least inpart on the information identifying the timing difference between theapparatus of the source base station and the target base station. Insome aspects, the source base station may perform or implement any oneor more of the aspects described in connection with the method, above orelsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in a non-transitory computer-readablemedium. The non-transitory computer-readable medium may store one ormore instructions for wireless communication. The one or moreinstructions, when executed by one or more processors of a source basestation, may cause the one or more processors to receive, from a UE,information identifying a timing difference between the source basestation and a target base station, wherein the timing difference betweenthe apparatus of the source base station and the target base station isassociated with a handover of the UE; and transmit informationidentifying a target base station timing advance value based at least inpart on the information identifying the timing difference between theapparatus of the source base station and the target base station. Insome aspects, the non-transitory computer-readable medium may implementany one or more of the aspects described in connection with the method,above or elsewhere herein.

Another innovative aspect of the subject matter described in thisdisclosure can be implemented in an apparatus for wirelesscommunication. The apparatus may include means for receiving, from a UE,information identifying a timing difference between the apparatus and atarget base station, wherein the timing difference between the apparatusof the source base station and the target base station is associatedwith a handover of the UE; and transmitting information identifying atarget base station timing advance value based at least in part on theinformation identifying the timing difference between the apparatus ofthe source base station and the target base station. In some aspects,the apparatus may include means for performing or implementing any oneor more of the aspects described in connection with the method, above orelsewhere herein.

Aspects generally include a method, apparatus, system, computer programproduct, non-transitory computer-readable medium, user equipment, basestation, wireless communication device, and processing system assubstantially described herein with reference to and as illustrated bythe accompanying drawings.

Details of one or more implementations of the subject matter describedin this disclosure are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram conceptually illustrating an example of awireless network.

FIG. 2 is a block diagram conceptually illustrating an example of a basestation (BS) in communication with a user equipment (UE) in a wirelessnetwork.

FIG. 3 is a diagram illustrating an example of timing advance for asource base station and a target base station.

FIG. 4 is a diagram illustrating an example of random access channel(RACH)-less timing advance determination.

FIG. 5 is a diagram illustrating another example of RACH-less timingadvance determination.

FIG. 6 is a diagram illustrating yet another example of RACH-less timingadvance determination.

FIG. 7 is a diagram illustrating still another example of RACH-lesstiming advance determination.

FIG. 8 is a diagram illustrating an example process performed, forexample, by a user equipment.

FIG. 9 is a diagram illustrating an example process performed, forexample, by a user equipment.

FIG. 10 is a diagram illustrating an example process performed, forexample, by a target base station.

FIG. 11 is a diagram illustrating an example process performed, forexample, by a source base station.

FIG. 12 is a diagram illustrating an example process performed, forexample, by a source base station.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

The following description is directed to certain implementations for thepurposes of describing the innovative aspects of this disclosure.However, a person having ordinary skill in the art will readilyrecognize that the teachings herein can be applied in a multitude ofdifferent ways. Some of the examples in this disclosure are based onwireless and wired local area network (LAN) communication according tothe Institute of Electrical and Electronics Engineers (IEEE) 802.11wireless standards, the IEEE 802.3 Ethernet standards, and the IEEE 1901Powerline communication (PLC) standards. However, the describedimplementations may be implemented in any device, system or network thatis capable of transmitting and receiving radio frequency signalsaccording to any of the wireless communication standards, including anyof the IEEE 802.11 standards, the Bluetooth® standard, code divisionmultiple access (CDMA), frequency division multiple access (FDMA), timedivision multiple access (TDMA), Global System for Mobile communications(GSM), GSM/General Packet Radio Service (GPRS), Enhanced Data GSMEnvironment (EDGE), Terrestrial Trunked Radio (TETRA), Wideband-CDMA(W-CDMA), Evolution Data Optimized (EV-DO), 1×EV-DO, EV-DO Rev A, EV-DORev B, High Speed Packet Access (HSPA), High Speed Downlink PacketAccess (HSDPA), High Speed Uplink Packet Access (HSUPA), Evolved HighSpeed Packet Access (HSPA+), Long Term Evolution (LTE), AMPS, or otherknown signals that are used to communicate within a wireless, cellularor internet of things (IOT) network, such as a system utilizing 3G, 4Gor 5G, or further implementations thereof, technology.

A base station (BS) and a user equipment (UE) may be associated with atiming advance or a transmission timing adjustment. “Timing advance,”“transmission timing adjustment,” and “timing advance value” may be usedinterchangeably herein. The timing advance may identify a timing offsetbetween the UE and the base station based at least in part onpropagation delay or other factors. For example, a timing advance mayidentify a negative offset, at the UE, between the start of a receiveddownlink subframe and a transmitted uplink subframe. This offset at theUE may ensure that the downlink and uplink subframes are synchronized atthe base station.

A handover is a procedure by which a UE is transferred from one cell(referred to as a source cell, where service may be provided by a sourcebase station) to another cell (referred to as a target cell, whereservice may be provided by a target base station). Some handovers areperformed using a random access channel (RACH) procedure (such as acontention-based RACH procedure or a contention-free RACH procedure),where the UE performs a RACH procedure with a target base station. In aRACH-based handover, the target base station may determine a timingadvance for the UE (relative to the target base station) based at leastin part on the RACH procedure, and may indicate the timing advance tothe UE as part of the RACH procedure.

Some handovers may be performed without using a RACH procedure. This mayeliminate RACH-related latency in the handover, thereby reducingmobility interruption time in proportion to the length of the RACHprocedure (such as approximately 10-12 milliseconds (ms) in some cases).It may be beneficial to determine a target base station timing advancevalue between the UE and the target base station using a non-RACH-basedtechnique, since the target base station may not be able to use the RACHprocedure to determine the timing advance. In some deployments,RACH-less handover has been restricted to synchronous deployments, orhas been subject to various restrictions (such as setting the targetbase station's timing advance to be equal to the source cell's timingadvance, or setting the target base station's timing advance to be zero,etc.).

Some techniques and apparatuses described herein provide determinationof a target base station timing advance value between a UE and targetbase station, such as in connection with a RACH-less handover procedure.For example, at least one of the UE, the target base station, or thesource base station may determine the target base station timing advancevalue without using a RACH procedure. In some aspects, the UE maydetermine the target base station's timing advance based at least inpart on a timing difference between the target base station and thesource base station and based at least in part on a timing offsetassociated with an uplink and a downlink of the UE. In some aspects, thetarget base station may determine the timing advance using an uplinkreference signal of the UE. In some aspects, the UE may report a timingdifference between the target base station and the source base station,and the source cell may determine a timing advance based at least inpart on the timing difference. In some aspects, the UE may report atiming difference between the target base station and the source basestation, and a base station (such as the source base station or thetarget base station) may determine a technique for determining thetiming advance based at least in part on the timing difference. Thesetechniques may be performed in various deployments irrespective ofwhether the target base station's timing advance is equal to the sourcebase station's timing advance or is zero.

Particular implementations of the subject matter described in thisdisclosure can be implemented to realize one or more of the followingpotential advantages. In some implementations, UE mobility is improved.Furthermore, interruption associated with a handover may be reducedthrough reduced handover latency. Still further, support for a RACH-lesshandover may be improved for base stations that do not share a sametiming advance value and for base stations associated with non-zerotiming advance values (such as base stations that provide large cells).

FIG. 1 is a block diagram conceptually illustrating an example of awireless network 100. The wireless network 100 may be an LTE network orsome other wireless network, such as a 5G or NR network. Wirelessnetwork 100 may include a number of BSs 110 (shown as BS 110 a, BS 110b, BS 110 c, and BS 110 d) and other network entities. A BS is an entitythat communicates with user equipment (UEs) and also may be referred toas a base station, a NR BS, a Node B, a gNB, a 5G node B (NB), an accesspoint, or a transmit receive point (TRP). Each BS may providecommunication coverage for a particular geographic area. In 3GPP, theterm “cell” can refer to a coverage area of a BS, a BS subsystem servingthis coverage area, or a combination thereof, depending on the contextin which the term is used.

ABS may provide communication coverage for a macro cell, a pico cell, afemto cell, another type of cell, or a combination thereof. A macro cellmay cover a relatively large geographic area (for example, severalkilometers in radius) and may allow unrestricted access by UEs withservice subscription. A pico cell may cover a relatively smallgeographic area and may allow unrestricted access by UEs with servicesubscription. A femto cell may cover a relatively small geographic area(for example, a home) and may allow restricted access by UEs havingassociation with the femto cell (for example, UEs in a closed subscribergroup (CSG)). A BS for a macro cell may be referred to as a macro BS.ABS for a pico cell may be referred to as a pico BS. A BS for a femtocell may be referred to as a femto BS or a home BS. A timing advancevalue for a BS may be expected to increase as the size of a cellprovided by the BS increases. In the example shown in FIG. 1, a BS 110 amay be a macro BS for a macro cell 102 a, a BS 110 b may be a pico BSfor a pico cell 102 b, and a BS 110 c may be a femto BS for a femto cell102 c. ABS may support one or multiple (for example, three) cells. Theterms “eNB”, “base station”, “NR BS”, “gNB”, “TRP”, “AP”, “node B”, “5GNB”, and “cell” may be used interchangeably herein.

In some examples, a cell may not necessarily be stationary, and thegeographic area of the cell may move according to the location of amobile BS. In some examples, the BSs may be interconnected to oneanother as well as to one or more other BSs or network nodes (not shown)in the wireless network 100 through various types of backhaulinterfaces, such as a direct physical connection, a virtual network, ora combination thereof using any suitable transport network.

Wireless network 100 also may include relay stations. A relay station isan entity that can receive a transmission of data from an upstreamstation (for example, a BS or a UE) and send a transmission of the datato a downstream station (for example, a UE or a BS). A relay stationalso may be a UE that can relay transmissions for other UEs. In theexample shown in FIG. 1, a relay station 110 d may communicate withmacro BS 110 a and a UE 120 d in order to facilitate communicationbetween BS 110 a and UE 120 d. A relay station also may be referred toas a relay BS, a relay base station, or a relay.

Wireless network 100 may be a heterogeneous network that includes BSs ofdifferent types, for example, macro BSs, pico BSs, femto BSs, relay BSs,and so on. These different types of BSs may have different transmitpower levels, different coverage areas, and different impacts oninterference in wireless network 100. For example, macro BSs may have ahigh transmit power level (for example, 5 to 40 Watts) whereas pico BSs,femto BSs, and relay BSs may have lower transmit power levels (forexample, 0.1 to 2 Watts).

A network controller 130 may couple to a set of BSs and may providecoordination and control for these BSs. Network controller 130 maycommunicate with the BSs via a backhaul. The BSs also may communicatewith one another, for example, directly or indirectly via a wireless orwireline backhaul.

UEs 120 (for example, 120 a, 120 b, 120 c) may be dispersed throughoutwireless network 100, and each UE may be stationary or mobile. A UE alsomay be referred to as an access terminal, a terminal, a mobile station,a subscriber unit, a station, or similar terms. A UE may be a cellularphone (for example, a smart phone), a personal digital assistant (PDA),a wireless modem, a wireless communication device, a handheld device, alaptop computer, a cordless phone, a wireless local loop (WLL) station,a tablet, a camera, a gaming device, a netbook, a smartbook, anultrabook, a medical device or equipment, biometric sensors/devices,wearable devices (smart watches, smart clothing, smart glasses, smartwrist bands, smart jewelry (for example, smart ring, smart bracelet)),an entertainment device (for example, a music or video device, or asatellite radio), a vehicular component or sensor, smart meters/sensors,industrial manufacturing equipment, a global positioning system device,or any other suitable device that is configured to communicate via awireless or wired medium.

Some UEs may be considered machine-type communication (MTC) or evolvedor enhanced machine-type communication (eMTC) UEs. MTC and eMTC UEsinclude, for example, robots, drones, remote devices, sensors, meters,monitors, location tags, or similar examples, that may communicate witha base station, another device (for example, remote device), or someother entity. A wireless node may provide, for example, connectivity foror to a network (for example, a wide area network such as Internet or acellular network) via a wired or wireless communication link. Some UEsmay be considered Internet-of-Things (IoT) devices or may be implementedas NB-IoT (narrowband internet of things) devices. Some UEs may beconsidered a Customer Premises Equipment (CPE). UE 120 may be includedinside a housing that houses components of UE 120, such as processorcomponents, memory components, similar components, or a combinationthereof.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular RAT andmay operate on one or more frequencies. A RAT also may be referred to asa radio technology, an air interface, or a wireless communicationtechnology. A frequency also may be referred to as a carrier, a channel,or a frequency channel. Each frequency may support a single RAT in agiven geographic area in order to avoid interference between wirelessnetworks of different RATs. In some cases, NR or 5G RAT networks may bedeployed.

In some examples, access to the air interface may be scheduled, where ascheduling entity (for example, a base station) allocates resources forcommunication among some or all devices and equipment within thescheduling entity's service area or cell. Within the present disclosure,as discussed further below, the scheduling entity may be responsible forscheduling, assigning, reconfiguring, and releasing resources for one ormore subordinate entities. That is, for scheduled communication,subordinate entities utilize resources allocated by the schedulingentity.

Base stations are not the only entities that may function as ascheduling entity. That is, in some examples, a UE may function as ascheduling entity, scheduling resources for one or more subordinateentities (for example, one or more other UEs). In this example, the UEis functioning as a scheduling entity, and other UEs utilize resourcesscheduled by the UE for wireless communication. A UE may function as ascheduling entity in a peer-to-peer (P2P) network, in a mesh network, oranother type of network. In a mesh network example, UEs may optionallycommunicate directly with one another in addition to communicating withthe scheduling entity.

Thus, in a wireless communication network with a scheduled access totime-frequency resources and having a cellular configuration, a P2Pconfiguration, and a mesh configuration, a scheduling entity and one ormore subordinate entities may communicate utilizing the scheduledresources.

In some aspects, two or more UEs 120 (for example, shown as UE 120 a andUE 120 e) may communicate directly using one or more sidelink channels(for example, without using a base station 110 as an intermediary tocommunicate with one another). For example, the UEs 120 may communicateusing peer-to-peer (P2P) communications, device-to-device (D2D)communications, a vehicle-to-everything (V2X) protocol (which mayinclude a vehicle-to-vehicle (V2V) protocol, a vehicle-to-infrastructure(V2I) protocol, or similar protocol), a mesh network, or similarnetworks, or combinations thereof. In this case, the UE 120 may performscheduling operations, resource selection operations, as well as otheroperations described elsewhere herein as being performed by the basestation 110.

FIG. 2 is a block diagram conceptually illustrating an example 200 of abase station 110 in communication with a UE 120. In some aspects, basestation 110 and UE 120 may respectively be one of the base stations andone of the UEs in wireless network 100 of FIG. 1. Base station 110 maybe equipped with T antennas 234 a through 234 t, and UE 120 may beequipped with R antennas 252 a through 252 r, where in general T≥1 andR≥1.

At base station 110, a transmit processor 220 may receive data from adata source 212 for one or more UEs, select one or more modulation andcoding schemes (MCS) for each UE based at least in part on channelquality indicators (CQIs) received from the UE, process (for example,encode and modulate) the data for each UE based at least in part on theMCS(s) selected for the UE, and provide data symbols for all UEs.Transmit processor 220 also may process system information (for example,for semi-static resource partitioning information (SRPI)) and controlinformation (for example, CQI requests, grants, and upper layersignaling) and provide overhead symbols and control symbols. Transmitprocessor 220 also may generate reference symbols for reference signals(for example, the cell-specific reference signal (CRS)) andsynchronization signals (for example, the primary synchronization signal(PSS) and secondary synchronization signal (SSS)). A transmit (TX)multiple-input multiple-output (MIMO) processor 230 may perform spatialprocessing (for example, precoding) on the data symbols, the controlsymbols, the overhead symbols, or the reference symbols, if applicable,and may provide T output symbol streams to T modulators (MODs) 232 athrough 232 t. Each modulator 232 may process a respective output symbolstream (for example, for OFDM) to obtain an output sample stream. Eachmodulator 232 may further process (for example, convert to analog,amplify, filter, and upconvert) the output sample stream to obtain adownlink signal. T downlink signals from modulators 232 a through 232 tmay be transmitted via T antennas 234 a through 234 t, respectively.According to various aspects described in more detail below, thesynchronization signals can be generated with location encoding toconvey additional information.

At UE 120, antennas 252 a through 252 r may receive the downlink signalsfrom base station 110 or other base stations and may provide receivedsignals to demodulators (DEMODs) 254 a through 254 r, respectively. Eachdemodulator 254 may condition (for example, filter, amplify,downconvert, and digitize) a received signal to obtain input samples.Each demodulator 254 may further process the input samples (for example,for OFDM) to obtain received symbols. A MIMO detector 256 may obtainreceived symbols from all R demodulators 254 a through 254 r, performMIMO detection on the received symbols if applicable, and providedetected symbols. A receive processor 258 may process (for example,demodulate and decode) the detected symbols, provide decoded data for UE120 to a data sink 260, and provide decoded control information andsystem information to a controller or processor (controller/processor)280. A channel processor may determine reference signal received power(RSRP), received signal strength indicator (RSSI), reference signalreceived quality (RSRQ), channel quality indicator (CQI), or othermeasurements. In some aspects, one or more components of UE 120 may beincluded in a housing.

On the uplink, at UE 120, a transmit processor 264 may receive andprocess data from a data source 262 and control information (forexample, for reports including RSRP, RSSI, RSRQ, or CQI) fromcontroller/processor 280. Transmit processor 264 also may generatereference symbols for one or more reference signals. The symbols fromtransmit processor 264 may be precoded by a TX MIMO processor 266 ifapplicable, further processed by modulators 254 a through 254 r (forexample, for DFT-s-OFDM or CP-OFDM), and transmitted to base station110. At base station 110, the uplink signals from UE 120 and other UEsmay be received by antennas 234, processed by demodulators 232, detectedby a MIMO detector 236 if applicable, and further processed by a receiveprocessor 238 to obtain decoded data and control information sent by UE120. Receive processor 238 may provide the decoded data to a data sink239 and the decoded control information to a controller or processor(controller/processor) 240. Base station 110 may include communicationunit 244 and communicate to network controller 130 via communicationunit 244. Network controller 130 may include communication unit 294, acontroller or processor (controller/processor) 290, and memory 292.

In some implementations, controller/processor 240 may be a component ofa processing system. A processing system may generally refer to a systemor series of machines or components that receives inputs and processesthe inputs to produce a set of outputs (which may be passed to othersystems or components of, for example, the UE 120). For example, aprocessing system of the UE 120 may refer to a system including thevarious other components or subcomponents of the UE 120.

The processing system of the UE 120 may interface with other componentsof the UE 120, and may process information received from othercomponents (such as inputs or signals), output information to othercomponents, etc. For example, a chip or modem of the UE 120 may includea processing system, a first interface to receive or obtain information,and a second interface to output, transmit or provide information. Insome cases, the first interface may refer to an interface between theprocessing system of the chip or modem and a receiver, such that the UE120 may receive information or signal inputs, and the information may bepassed to the processing system. In some cases, the second interface mayrefer to an interface between the processing system of the chip or modemand a transmitter, such that the UE 120 may transmit information outputfrom the chip or modem. A person having ordinary skill in the art willreadily recognize that the second interface also may obtain or receiveinformation or signal inputs, and the first interface also may output,transmit or provide information.

In some implementations, controller/processor 280 may be a component ofa processing system. A processing system may generally refer to a systemor series of machines or components that receives inputs and processesthe inputs to produce a set of outputs (which may be passed to othersystems or components of, for example, the BS 110). For example, aprocessing system of the BS 110 may refer to a system including thevarious other components or subcomponents of the BS 110.

The processing system of the BS 110 may interface with other componentsof the BS 110, and may process information received from othercomponents (such as inputs or signals), output information to othercomponents, etc. For example, a chip or modem of the BS 110 may includea processing system, a first interface to receive or obtain information,and a second interface to output, transmit or provide information. Insome cases, the first interface may refer to an interface between theprocessing system of the chip or modem and a receiver, such that the BS110 may receive information or signal inputs, and the information may bepassed to the processing system. In some cases, the second interface mayrefer to an interface between the processing system of the chip or modemand a transmitter, such that the BS 110 may transmit information outputfrom the chip or modem. A person having ordinary skill in the art willreadily recognize that the second interface also may obtain or receiveinformation or signal inputs, and the first interface also may output,transmit or provide information.

Controller/processor 240 of base station 110, controller/processor 280of UE 120, or any other component(s) of FIG. 2 may perform one or moretechniques associated with a RACH-less timing advance determination, asdescribed in more detail elsewhere herein. For example,controller/processor 240 of base station 110, controller/processor 280of UE 120, or any other component(s) (or combinations of components) ofFIG. 2 may perform or direct operations of, for example, processes 800through 1200 of FIGS. 8 through 12, respectively, or other processes asdescribed herein. Memories 242 and 282 may store data and program codesfor base station 110 and UE 120, respectively. A scheduler 246 mayschedule UEs for data transmission on the downlink, the uplink, or acombination thereof.

The stored program codes, when executed by controller/processor 280 orother processors and modules at UE 120, may cause the UE 120 to performoperations described with respect to process 800 of FIG. 8, process 900of FIG. 9, or other processes as described herein. The stored programcodes, when executed by controller/processor 240 or other processors andmodules at base station 110, may cause the base station 110 to performoperations described with respect to process 1000 of FIG. 10, process1100 of FIG. 11, process 1200 of FIG. 12, or other processes asdescribed herein. A scheduler 246 may schedule UEs for data transmissionon the downlink, the uplink, or a combination thereof.

In some aspects, UE 120 may include means for receiving informationidentifying a timing offset associated with UL and DL communications ofthe UE; means for determining a target base station timing advance valuefor a handover to a target base station based at least in part on atleast one of the information identifying the timing offset, a timingdifference between the target base station and a source base stationassociated with the UE, or a source base station timing advance valueassociated with the source base station; means for determining thetiming difference between the target base station and a source basestation based at least in part on reference signaling received from thesource base station and the target base station; means for transmittingat least one of: information identifying a timing difference between atarget base station and a source base station associated with ahandover, or an uplink reference signal; means for receiving informationidentifying a target base station timing advance value, where theinformation identifying the target base station timing advance value isbased at least in part on the timing difference between the target basestation and the source base station or the uplink reference signal; orcombinations thereof. In some aspects, such means may include one ormore components of UE 120 described in connection with FIG. 2, such asan apparatus of UE 120.

In some aspects, base station 110 may include means for receiving, froma UE, at least one of: information identifying a timing differencebetween the target base station and a source base station, where thetarget base station and the source base station are associated with ahandover of a UE, or an uplink reference signal; means for providing, tothe UE, information identifying a target base station timing advancevalue, where the target base station timing advance value is based atleast in part on the information identifying the timing difference orthe uplink reference signal; means for determining the target basestation timing advance value based at least in part on the informationidentifying the timing difference between the apparatus of the targetbase station and the source base station or the uplink reference signal;means for selecting a technique for determining the target base stationtiming advance value based at least in part on the informationidentifying the timing difference between the apparatus of the targetbase station and the source base station or the uplink reference signal;means for determining the target base station timing advance value aszero; means for determining the target base station timing advance valuein accordance with a source base station timing advance value associatedwith the source base station; means for determining the target basestation timing advance value using the uplink reference signal; meansfor providing, to the source base station to be transmitted to the UE,the information identifying the target base station timing advancevalue; means for determining a timing offset of a user equipment (UE),wherein the timing offset is based at least in part on a differencebetween a downlink propagation delay and an uplink propagation delay ofthe UE; means for transmitting, to the UE in connection with a handoverof the UE from the apparatus of the source base station to a target basestation, information identifying the timing offset t; means forreceiving, from a user equipment (UE), information identifying a timingdifference between the apparatus of the source base station and a targetbase station, wherein the timing difference between the apparatus of thesource base station and the target base station is associated with ahandover of the UE; means for transmitting information identifying atarget base station timing advance value based at least in part on theinformation identifying the timing difference between the apparatus ofthe source base station and the target base station; means fordetermining the target base station timing advance value based at leastin part on the information identifying the timing difference between theapparatus of the source base station and the target base station; meansfor selecting a technique for determining the target base station timingadvance value based at least in part on the information identifying thetiming difference between the apparatus of the source base station andthe target base station; or combinations thereof. In some aspects, suchmeans may include one or more components of base station 110 describedin connection with FIG. 2, such as an apparatus of base station 110.

While blocks in FIG. 2 are illustrated as distinct components, thefunctions described above with respect to the blocks may be implementedin a single hardware, software, or combination component or in variouscombinations of components. For example, the functions described withrespect to the transmit processor 264, the receive processor 258, the TXMIMO processor 266, or another processor may be performed by or underthe control of controller/processor 280.

FIG. 3 is a diagram illustrating an example 300 of timing advance for asource base station and a target base station. As shown in FIG. 3, andby reference numbers 310 and 320, a source BS 110-1 and a target BS110-2 may provide respective reference signals to a UE 120. For example,the respective reference signals may include a demodulation referencesignal, a phase tracking reference signal, a channel state informationreference signal, or another reference signal. The UE 120 may use therespective reference signals to identify a timing difference between thesource BS 110-1 and the target BS 110-2.

Respective subframe timings of source BS 110-1 and target BS 110-2 areshown by reference numbers 330 and 340. These subframe timings areprovided as examples, and the techniques and apparatuses describedherein may be used to identify a timing difference based at least inpart on any set of subframe timings (such as different than the subframetiming shown).

The UE 120 may determine a timing difference 350 between the source BS110-1 and the target BS 110-2 based at least in part on the respectivereference signals. For example, the UE 120 may determine a referencesignal timing difference (RSTD) value between the source BS 110-1 andthe target BS 110-2 by identifying start times of subframes of thesource BS 110-1 and the target BS 110-2 based at least in part on therespective reference signals. In some aspects, the UE 120 may determinethe timing difference 350 as a difference between respective start timesof subframes of the source BS 110-1 and the target BS 110-2. Forexample, RSTD may be defined as T_(target)−T_(source), where T_(target)is a time at which the UE 120 receives a start of a particular subframefrom the target BS 110-2 and T_(source) is a time at which the UE 120receives a start of a subframe that is closest in time to the particularsubframe from the source BS 110-1. At least one of the UE 120, thesource BS 110-1, or the target BS 110-2 may use the timing difference350 to determine a timing offset between the UE 120 and the target BS110-2, as described in more detail elsewhere herein.

FIG. 4 is a diagram illustrating an example 400 of random access channel(RACH)-less timing advance determination. As shown, the example 400includes a UE 120, a source BS 110-1, and a target BS 110-2. As shown inFIG. 4, and as described in more detail in connection with FIG. 3,source BS 110-1 and target BS 110-2 may provide respective referencesignals to the UE 120. As shown by reference number 410, and asdescribed in more detail in connection with FIG. 3, the UE 120 maydetermine a timing difference (such as timing difference 350 or RSTD)between the source BS 110-1 and the target BS 110-2 using the respectivereference signals of the source BS 110-1 and the target BS 110-2.

As shown by reference number 420, the UE 120 may receive informationidentifying a timing offset from source BS 110-1. The timing offset mayidentify a difference between an uplink timing and a downlink timing ofthe UE 120. For example, the timing offset may identify a timingmis-alignment between the uplink and the downlink due to a difference inpropagation delay (since the uplink and the downlink are likely topropagate via different paths), a switching time from transmitting toreceiving or vice versa, a hardware constraint of the UE 120 or a BS110, a propagation delay between transmit and reception, or a similarcause of timing mis-alignment. The timing offset may be representedherein using the variable M. In some aspects, the source BS 110-1 mayprovide the information identifying the timing offset in a handovercommand, such as a radio resource control (RRC) connectionreconfiguration message.

In some aspects, a granularity of the timing offset may be based atleast in part on a numerology of the target BS 110-2, such as anumerology of a physical uplink shared channel (PUSCH) for the target BS110-2 or a numerology of an uplink bandwidth part of the target BS110-2. For example, the timing offset may use a more granular or moreprecise value for a numerology associated with a shorter slot lengththan for a numerology associated with a longer slot length. Thus, thesource BS 110-1 may conserve signalling resources that would otherwisebe used to signal an unnecessarily precise timing offset.

As shown by reference number 430, the UE 120 may determine a target basestation timing advance value associated with the target BS 110-2 usingthe timing offset, the timing difference, and a source base stationtiming advance value associated with the source BS 110-1. For example,the UE 120 may determine the timing advance value for the source BS110-1 based at least in part on communicating with the source BS 110-1or based at least in part on receiving information identifying thetiming advance value for the source BS 110-1. The timing advance valuefor the source BS 110-1 may be represented as TA_(source). In someaspects, the UE 120 may determine the timing advance value for thesource BS 110-1, TA_(target), as TA_(target)=TA_(source) RSTD+Δτ.

As shown by reference number 440, the UE 120 may perform the handover tothe target BS 110-2 based at least in part on the target BS 110-2'stiming advance. For example, the UE 120 may perform the handover withoutperforming a RACH procedure with regard to the target BS 110-2. In thisway, the UE 120 may determine the timing advance value for the target BS110-2 based at least in part on the timing advance value for the sourceBS 110-1, the timing difference between the source BS 110-1 and thetarget BS 110-2, and the timing offset of the UE 120. Thus, the UE 120may determine the timing advance value for the target BS 110-2 withoutreceiving explicit signalling identifying the timing advance value forthe target BS 110-2 and without performing a RACH procedure as part ofthe handover, thereby reducing latency and user interruption associatedwith the handover.

FIG. 5 is a diagram illustrating another example 500 of RACH-less timingadvance determination. The example 500 is where the target BS 110-2determines the target BS timing advance based at least in part on anuplink reference signal of the UE 120.

As shown in FIG. 5, and by reference number 510, the UE 120 may providean uplink (UL) reference signal to the target BS 110-2. For example, theuplink reference signal may include a sounding reference signal (SRS)(such as an SRS associated with a multiple-input multiple-output (MIMO)operation), a reference signal for a positioning purpose, or anotherreference signal.

As shown by reference number 520, the target BS 110-2 may determine thetarget BS timing advance based at least in part on the uplink referencesignal. For example, the target BS 110-2 may determine a time at whichthe uplink reference signal was transmitted, and may determine adifference between the time at which the uplink reference signal wastransmitted and a time at which the target BS 110-2 receives the uplinkreference signal. Thus, the target BS 110-2 may determine the target BStiming advance without knowledge of the source BS timing advance andwithout performing a RACH procedure with the UE 120, thereby reducinglatency of handover.

As shown by reference number 530, the source BS 110-1 may provideinformation identifying the target BS timing advance to the UE 120. Forexample, the target BS 110-2 may provide information identifying thetarget BS timing advance to the source BS 110-1, and the source BS 110-1may provide this information to the UE 120. In some aspects, theinformation identifying the target BS timing advance may be provided ina handover command. In some aspects, the target BS 110-2 may provide theinformation identifying the target BS timing advance to the source BS110-1. As shown by reference number 540, the UE 120 may perform thehandover to the target BS based at least in part on the target BS timingadvance.

FIG. 6 is a diagram illustrating yet another example 600 of RACH-lesstiming advance determination. In the example 600, the source BS 110-1determines the target BS timing advance. As shown in FIG. 6, and byreference number 610, the UE 120 may determine a timing differencebetween the source BS 110-1 and the target BS 110-2 using the respectivereference signals of the source BS 110-1 and the target BS 110-2. Asshown by reference number 620, the UE 120 may provide informationidentifying the timing difference to, for example, the source BS 110-1.In some aspects, the UE 120 may provide a quantization of the timingdifference. For example, the UE 120 may provide a b-bit quantization ora different type of quantization of the timing difference, therebyconserving signaling resources that would otherwise be used to provideinformation identifying the timing difference at a sample-timegranularity or another, more complex granularity than the quantization.In some aspects, the UE 120 may provide the information identifying thetiming difference in a radio resource management (RRM) report.

As shown by reference number 630, the source BS 110-1 may determine thetarget BS timing advance using the timing difference and a source BStiming advance for the UE 120. In some aspects, the source BS 110-1 maydetermine the target BS timing advance based at least in part on atiming offset (Δτ), which may improve the accuracy of the target BStiming advance relative to a case where the source BS 110-1 does nottake into account the timing offset. In such a case, the source BS 110-1may determine the target BS timing advance as TA_(target)=TA_(source)RSTD+Δτ. In some aspects, the source BS 110-1 may determine the targetBS timing advance without using the timing offset, which may simplifydetermination of the target BS timing advance.

As shown by reference number 640, the source BS 110-1 may provideinformation identifying the target BS timing advance to the UE 120. Forexample, the source BS 110-1 may provide the information identifying thetarget BS timing advance in a handover command, as described in moredetail elsewhere herein. As further shown, the UE 120 may perform thehandover to the target BS 110-2 based at least in part on the target BStiming advance value, thereby reducing latency of the handover relativeto a handover that uses a RACH procedure to determine the target BStiming advance value.

FIG. 7 is a diagram illustrating still another example 700 of RACH-lesstiming advance determination. In the example 700, a BS 110 selects atechnique for determining the target BS timing advance based at least inpart on a timing difference between the source BS 110-1 and the targetBS 110-2. In some aspects, at least some of the operations described inexample 700 may be performed by the source BS 110-1 (as shown in FIG.7). In some aspects, at least some of the operations described inexample 700 may be performed by the target BS 110-2 (not shown in FIG.7).

As shown in FIG. 7, and by reference number 710, the UE 120 may provideinformation identifying a timing difference to the source BS 110-1. Forexample, and as shown, the UE 120 may determine the timing differencebased at least in part on reference signals of the source BS 110-1 andthe target BS 110-2. In some aspects, the UE 120 may provide aquantization of the timing difference to the source BS 110-1. In someaspects, the UE 120 may provide the information identifying the timingdifference to the target BS 110-2.

As shown by reference number 720, the source BS 110-1 (or the target BS110-2) may select a technique for determining the target BS timingadvance based at least in part on the timing difference. For example,the technique may include determining the target BS timing advance aszero, determining the target BS timing advance in accordance with asource base station timing advance value for the source BS 110-1, ordetermining the target BS timing advance using an uplink referencesignal (as described in more detail in connection with example 400). Insome aspects, the source BS 110-1 may select the technique based atleast in part on the timing difference. For example, the source BS 110-1may determine whether the timing difference is in a first range of zeroto X1, a second range of X1 to X2, or a third range of greater than X2.When the timing difference is in the first range, the source BS 110-1may determine that the target BS timing advance is to be determined inaccordance with the timing advance value for the source BS 110-1. Whenthe timing difference is in the second range, the source BS 110-1 maydetermine that the target BS timing advance is to be determined as zero.When the timing difference is in the third range, the source BS 110-1may determine that the target BS timing advance is to be determinedusing an uplink reference signal.

As shown by reference number 730, the source BS 110-1 (or the target BS110-2) may provide information identifying the target BS timing advanceor the technique to be used to determine the target BS timing advance.Accordingly, the UE 120 may determine the target BS timing advance aszero, or may determine the target BS timing advance as equal to thesource BS timing advance. Additionally, or alternatively, the UE 120 maytransmit an uplink reference signal to be used by the target BS 110-2 todetermine the target BS timing advance. Thus, a BS 110 (such as thesource BS 110-1 or the target BS 110-2) may determine the technique tobe used based at least in part on the timing difference between thesource BS 110-1 and the target BS 110-2, thereby improving flexibilityof timing advance determination and conserving resources that might beused to perform an uplink reference signal-based timing advancedetermination.

FIG. 8 is a diagram illustrating an example process 800 performed, forexample, by a UE. The process 800 shows an example where a UE (forexample, UE 120) performs a RACH-less timing advance determination. Insome aspects, the process 800 may be performed by an apparatus of a UE,which may include one or more interfaces and a processing system, asdescribed elsewhere herein.

As shown in FIG. 8, in some aspects, the process 800 may includereceiving information identifying a timing offset associated with uplinkand downlink communications of the UE (block 810). For example, the UE(such as using antenna 252, DEMOD 254, MIMO detector 256, receiveprocessor 258, or controller/processor 280) may receive informationidentifying a timing offset associated with uplink and downlinkcommunications of the UE. In some aspects, the timing offset may bereferred to herein as Δτ.

As shown in FIG. 8, in some aspects, the process 800 may includedetermining a target base station timing advance value for a handover tothe target base station based at least in part on at least one of theinformation identifying the timing offset, a timing difference betweenthe target base station and a source base station associated with theUE, or a source base station timing advance value associated with thesource base station (block 820). For example, the UE (such as usingcontroller/processor 280) may determine a target base station timingadvance associated with a handover to a target base station. The UE maydetermine the timing advance based at least in part on at least one ofthe information identifying the timing offset, a timing differencebetween the target base station and a source base station associatedwith the UE, or a source base station timing advance value associatedwith the source base station.

The process 800 may include additional aspects, such as any singleaspect or any combination of aspects described below or in connectionwith one or more other processes described elsewhere herein.

In a first aspect, the timing difference is based at least in part on areference signal timing difference between the target base station andthe source base station. In a second aspect, alone or in combinationwith the first aspect, the UE may determine the timing differencebetween the target base station and the source base station based atleast in part on reference signaling received from the source basestation and the target base station.

In a third aspect, alone or in combination with one or more of the firstand second aspects, the timing offset is based at least in part on aswitching time (e.g., a transmit-to-receive switching time and/or thelike), a propagation delay between transmit and reception, or a hardwareconfiguration of at least one of the UE, the source base station, or thetarget base station. In a fourth aspect, alone or in combination withone or more of the first through third aspects, a granularity of thetiming offset is based at least in part on at least one of a numerology,or a slot length of the target base station. In a fifth aspect, alone orin combination with one or more of the first through fourth aspects, theinformation identifying the timing offset is received in a handovercommand. In a sixth aspect, alone or in combination with one or more ofthe first through fifth aspects, the target base station timing advancevalue is determined without performing a random access procedure (a RACHprocedure). In a seventh aspect, alone or in combination with one ormore of the first through sixth aspects, the target base station timingadvance value is determined based at least in part on the informationidentifying the timing offset, the timing difference between the targetbase station and the source base station, and the source base stationtiming advance value.

Although FIG. 8 shows example blocks of the process 800, in someaspects, the process 800 may include additional blocks, fewer blocks,different blocks, or differently arranged blocks than those depicted inFIG. 8. Additionally, or alternatively, two or more of the blocks of theprocess 800 may be performed in parallel.

FIG. 9 is a diagram illustrating an example process 900 performed, forexample, by a UE. The process 900 shows an example where a UE (forexample, UE 120) performs a RACH-less timing advance determination. Insome aspects, the process 900 may be performed by an apparatus of a UE,which may include one or more interfaces and a processing system, asdescribed elsewhere herein.

As shown in FIG. 9, in some aspects, the process 900 may includetransmitting at least one of: information identifying a timingdifference for a handover between a target base station and a sourcebase station, or an uplink reference signal (block 910). For example,the UE (such as using controller/processor 280, transmit processor 264,TX MIMO processor 266, MOD 254, or antenna 252) may transmit informationidentifying a timing difference for a handover between a target basestation and a source base station (e.g., from the source base station tothe target base station). In some aspects, the UE may transmit an uplinkreference signal.

As shown in FIG. 9, in some aspects, the process 900 may includereceiving information identifying a target base station timing advancevalue, where the information identifying the target base station timingadvance value is based at least in part on the timing difference betweenthe target base station and the source base station or the uplinkreference signal (block 920). For example, the UE (such as using antenna252, DEMOD 254, MIMO detector 256, receive processor 258, orcontroller/processor 280) may receive information identifying a targetbase station timing advance value. The information identifying thetarget base station timing advance value may be based at least in parton the timing difference between the target base station and the sourcebase station or the uplink reference signal.

The process 900 may include additional aspects, such as any singleaspect or any combination of aspects described below or in connectionwith one or more other processes described elsewhere herein.

In a first aspect, the handover is performed without performing a randomaccess procedure. In a second aspect, alone or in combination with thefirst aspect, the information identifying the timing difference betweenthe target base station and the source base station is a quantization ofthe timing difference between the target base station and the sourcebase station. In a third aspect, alone or in combination with the firstand second aspects, the information identifying the timing differencebetween the target base station and the source base station is providedin a radio resource management report. In a fourth aspect, alone or incombination with one or more of the first through third aspects, theuplink reference signal includes a sounding reference signal.

Although FIG. 9 shows example blocks of the process 900, in someaspects, the process 900 may include additional blocks, fewer blocks,different blocks, or differently arranged blocks than those depicted inFIG. 9. Additionally, or alternatively, two or more of the blocks of theprocess 900 may be performed in parallel.

FIG. 10 is a diagram illustrating an example process 1000 performed, forexample, by a target base station. The process 1000 is an example wherea target base station (for example, BS 110) performs a RACH-less timingadvance base station. In some aspects, the process 1000 may be performedby an apparatus of a UE, which may include one or more interfaces and aprocessing system, as described elsewhere herein.

As shown in FIG. 10, in some aspects, the process 1000 may includereceiving, from a UE, at least one of: information identifying a timingdifference between the apparatus of the target base station and a sourcebase station, where the apparatus of the target base station and thesource base station are associated with a handover of the UE, or anuplink reference signal (block 1010). For example, the target basestation (such as using antenna 234, DEMOD 232, MIMO detector 236,receive processor 238, or controller/processor 240) may receive, from aUE (such as UE 120) information identifying a timing difference betweenthe apparatus of the target base station and a source base station, oran uplink reference signal. The apparatus of the target base station andthe source base station may be associated with a handover of the UE(e.g., from the source base station to the target base station).

As shown in FIG. 10, in some aspects, the process 1000 may includeproviding, to the UE, information identifying a target base stationtiming advance value for the target base station, where the target basestation timing advance is based at least in part on the informationidentifying the timing difference or the uplink reference signal (block1020). For example, the target base station (such as usingcontroller/processor 240, transmit processor 220, TX MIMO processor 230,MOD 232, or antenna 234) may provide, to the UE, information identifyinga target base station timing advance value. The target base stationtiming advance value may be based at least in part on informationidentifying the timing difference between the target base station andthe source base station or the uplink reference signal.

The process 1000 may include additional aspects, such as any singleaspect or any combination of aspects described below or in connectionwith one or more other processes described elsewhere herein.

In a first aspect, the information identifying the timing differencebetween the apparatus of the target base station and the source basestation is a quantization of the timing difference between the apparatusof the target base station and the source base station. In a secondaspect, alone or in combination with the first aspect, the informationidentifying the timing difference between the apparatus of the targetbase station and the source base station is received in a radio resourcemanagement report. In a third aspect, alone or in combination with oneor more of the first and second aspects, the uplink reference signalincludes a sounding reference signal. In a fourth aspect, alone or incombination with one or more of the first through third aspects, thetarget base station may determine the target base station timing advancevalue based at least in part on the information identifying the timingdifference between the apparatus of the target base station and thesource base station or the uplink reference signal. In a fifth aspect,alone or in combination with one or more of the first through fourthaspects, the target base station may select a technique for determiningthe target base station timing advance value based at least in part onthe information identifying the timing difference between the apparatusof the target base station and the source base station or the uplinkreference signal. In a sixth aspect, alone or in combination with one ormore of the first through fifth aspects, the technique is selected froma plurality of techniques including at least one of determining thetarget base station timing advance value as zero, determining the targetbase station timing advance value in accordance with a source basestation timing advance value associated with the source base station, ordetermining the target base station timing advance value using theuplink reference signal. In a seventh aspect, alone or in combinationwith one or more of the first through sixth aspects, the target basestation may provide, to the source base station to be transmitted to theUE, the information identifying the target base station timing advancevalue. In an eighth aspect, alone or in combination with one or more ofthe first through seventh aspects, the handover is performed withoutperforming a random access procedure.

Although FIG. 10 shows example blocks of the process 1000, in someaspects, the process 1000 may include additional blocks, fewer blocks,different blocks, or differently arranged blocks than those depicted inFIG. 10. Additionally, or alternatively, two or more of the blocks ofthe process 1000 may be performed in parallel.

FIG. 11 is a diagram illustrating an example process 1100 performed, forexample, by a source base station. The process 1100 is an example wherea source base station (for example, BS 110) performs a RACH-less timingadvance determination. In some aspects, the process 1100 may beperformed by an apparatus of a base station, which may include one ormore interfaces and a processing system, as described elsewhere herein.

As shown in FIG. 11, in some aspects, the process 1100 may includedetermining a timing offset of a UE, where the timing offset is based atleast in part on a difference between a downlink propagation delay andan uplink propagation delay of the UE (block 1110). For example, thesource base station (such as using controller/processor 240) maydetermine a timing offset of a UE. The timing offset may be based atleast in part on a difference between a downlink propagation delay andan uplink propagation delay of the UE.

As shown in FIG. 11, in some aspects, the process 1100 may includetransmitting, to the UE in connection with a handover of the UE from theapparatus of the source base station to a target base station,information identifying the timing offset (block 1120). For example, thesource base station (such as using controller/processor 240, transmitprocessor 220, TX MIMO processor 230, MOD 232, or antenna 234) maytransmit, to the UE in connection with the handover of the UE from thesource base station to a target base station, information identifyingthe timing offset.

The process 1100 may include additional aspects, such as any singleaspect or any combination of aspects described below or in connectionwith one or more other processes described elsewhere herein.

In a first aspect, the timing offset is based at least in part on aswitching time, a propagation delay between transmit and reception, or ahardware configuration of at least one of the UE, the source basestation, or the target base station. In a second aspect, alone or incombination with the first aspect, the information identifying thetiming offset is transmitted in connection with a handover command. In athird aspect, alone or in combination with one or more of the first andsecond aspects, a granularity of the timing offset is based at least inpart on a numerology or a slot length of the target base station.

Although FIG. 11 shows example blocks of the process 1100, in someaspects, the process 1100 may include additional blocks, fewer blocks,different blocks, or differently arranged blocks than those depicted inFIG. 11. Additionally, or alternatively, two or more of the blocks ofthe process 1100 may be performed in parallel.

FIG. 12 is a diagram illustrating an example process 1200 performed, forexample, by a source base station. The process 1200 is an example wherea source base station (for example, BS 110) performs a RACH-less timingadvance determination. In some aspects, the process 1200 may beperformed by an apparatus of a base station, which may include one ormore interfaces and a processing system, as described elsewhere herein.

As shown in FIG. 12, in some aspects, the process 1200 may includereceiving, from a UE, information identifying a timing differencebetween the apparatus of the source base station and a target basestation, where the timing difference is associated with a handover ofthe UE (block 1210). For example, the source base station (such as usingantenna 234, DEMOD 232, MIMO detector 236, receive processor 238, orcontroller/processor 240) may receive, from a UE, informationidentifying a timing difference between the apparatus of the source basestation and a target base station. The timing difference may beassociated with a handover of the UE.

As shown in FIG. 12, in some aspects, the process 1200 may includetransmitting information identifying a target base station timingadvance value based at least in part on the information identifying thetiming difference between the apparatus of the source base station andthe target base station (block 1220). For example, the source basestation (such as using controller/processor 240, transmit processor 220,TX MIMO processor 230, MOD 232, or antenna 234) may transmit informationidentifying a target base station timing advance value based at least inpart on the information identifying the timing difference between theapparatus of the source base station and the target base station.

The process 1200 may include additional aspects, such as any singleaspect or any combination of aspects described below or in connectionwith one or more other processes described elsewhere herein.

In a first aspect, the information identifying the timing differencebetween the apparatus of the source base station and the target basestation is a quantization of the timing difference. In a second aspect,alone or in combination with the first aspect, the informationidentifying the timing difference between the apparatus of the sourcebase station and the target base station is received in a radio resourcemanagement report. In a third aspect, alone or in combination with oneor more of the first and second aspects, the information identifying thetarget base station timing advance value is transmitted in connectionwith a handover command. In a fourth aspect, alone or in combinationwith one or more of the first through third aspects, the source basestation may determine the target base station timing advance value basedat least in part on the information identifying the timing differencebetween the apparatus of the source base station and the target basestation. In a fifth aspect, alone or in combination with one or more ofthe first through fourth aspects, the source base station may select atechnique for determining the target base station timing advance valuebased at least in part on the information identifying the timingdifference between the apparatus of the source base station and thetarget base station. In a sixth aspect, alone or in combination with oneor more of the first through fifth aspects, the technique is selectedfrom a plurality of techniques including at least one of determining thetarget base station timing advance value as zero, determining the targetbase station timing advance value in accordance with a source basestation timing advance value associated with the apparatus of the sourcebase station, or determining the target base station timing advancevalue using the uplink reference signal.

Although FIG. 12 shows example blocks of the process 1200, in someaspects, the process 1200 may include additional blocks, fewer blocks,different blocks, or differently arranged blocks than those depicted inFIG. 12. Additionally, or alternatively, two or more of the blocks ofthe process 1200 may be performed in parallel.

The foregoing disclosure provides illustration and description, but isnot intended to be exhaustive or to limit the aspects to the preciseform disclosed. Modifications and variations may be made in light of theabove disclosure or may be acquired from practice of the aspects.

As used herein, the term “component” is intended to be broadly construedas hardware, firmware, or a combination of hardware and software. Asused herein, a processor is implemented in hardware, firmware, or acombination of hardware and software.

Some aspects are described herein in connection with thresholds. As usedherein, satisfying a threshold may refer to a value being greater thanthe threshold, greater than or equal to the threshold, less than thethreshold, less than or equal to the threshold, equal to the threshold,not equal to the threshold, or the like.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: a, b, or c” is intended to cover: a, b, c,a-b, a-c, b-c, and a-b-c.

The various illustrative logics, logical blocks, modules, circuits andalgorithm processes described in connection with the aspects disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. The interchangeability of hardware and softwarehas been described generally, in terms of functionality, and illustratedin the various illustrative components, blocks, modules, circuits andprocesses described above. Whether such functionality is implemented inhardware or software depends upon the particular application and designconstraints imposed on the overall system.

The hardware and data processing apparatus used to implement the variousillustrative logics, logical blocks, modules and circuits described inconnection with the aspects disclosed herein may be implemented orperformed with a general purpose single- or multi-chip processor, adigital signal processor (DSP), an application specific integratedcircuit (ASIC), a field programmable gate array (FPGA) or otherprogrammable logic device, discrete gate or transistor logic, discretehardware components, or any combination thereof designed to perform thefunctions described herein. A general purpose processor may be amicroprocessor, or, any conventional processor, controller,microcontroller, or state machine. A processor also may be implementedas a combination of computing devices, for example, a combination of aDSP and a microprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration. In some aspects, particular processes and methods may beperformed by circuitry that is specific to a given function.

In one or more aspects, the functions described may be implemented inhardware, digital electronic circuitry, computer software, firmware,including the structures disclosed in this specification and theirstructural equivalents thereof, or in any combination thereof. Aspectsof the subject matter described in this specification also can beimplemented as one or more computer programs, i.e., one or more modulesof computer program instructions, encoded on a computer storage mediafor execution by, or to control the operation of, data processingapparatus.

If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. The processes of a method or algorithmdisclosed herein may be implemented in a processor-executable softwaremodule which may reside on a computer-readable medium. Computer-readablemedia includes both computer storage media and communication mediaincluding any medium that can be enabled to transfer a computer programfrom one place to another. A storage media may be any available mediathat may be accessed by a computer. By way of example, and notlimitation, such computer-readable media may include RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium that may be used to storedesired program code in the form of instructions or data structures andthat may be accessed by a computer. Also, any connection can be properlytermed a computer-readable medium. Disk and disc, as used herein,includes compact disc (CD), laser disc, optical disc, digital versatiledisc (DVD), floppy disk, and Blu-ray disc where disks usually reproducedata magnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media. Additionally, the operations of a method oralgorithm may reside as one or any combination or set of codes andinstructions on a machine readable medium and computer-readable medium,which may be incorporated into a computer program product.

Various modifications to the aspects described in this disclosure may bereadily apparent to those skilled in the art, and the generic principlesdefined herein may be applied to other aspects without departing fromthe spirit or scope of this disclosure. Thus, the claims are notintended to be limited to the aspects shown herein, but are to beaccorded the widest scope consistent with this disclosure, theprinciples and the novel features disclosed herein.

Additionally, a person having ordinary skill in the art will readilyappreciate, the terms “upper” and “lower” are sometimes used for ease ofdescribing the figures, and indicate relative positions corresponding tothe orientation of the figure on a properly oriented page, and may notreflect the proper orientation of any device as implemented.

Certain features that are described in this specification in the contextof separate aspects also can be implemented in combination in a singleaspect. Conversely, various features that are described in the contextof a single aspect also can be implemented in multiple aspectsseparately or in any suitable subcombination. Moreover, althoughfeatures may be described above as acting in certain combinations andeven initially claimed as such, one or more features from a claimedcombination can in some cases be excised from the combination, and theclaimed combination may be directed to a subcombination or variation ofa subcombination.

Similarly, while operations are depicted in the drawings in a particularorder, this should not be understood as requiring that such operationsbe performed in the particular order shown or in sequential order, orthat all illustrated operations be performed, to achieve desirableresults. Further, the drawings may schematically depict one more exampleprocesses in the form of a flow diagram. However, other operations thatare not depicted can be incorporated in the example processes that areschematically illustrated. For example, one or more additionaloperations can be performed before, after, simultaneously, or betweenany of the illustrated operations. In certain circumstances,multitasking and parallel processing may be advantageous. Moreover, theseparation of various system components in the aspects described aboveshould not be understood as requiring such separation in all aspects,and it should be understood that the described program components andsystems can generally be integrated together in a single softwareproduct or packaged into multiple software products. Additionally, otheraspects are within the scope of the following claims. In some cases, theactions recited in the claims can be performed in a different order andstill achieve desirable results.

What is claimed is:
 1. A method of wireless communication performed byan apparatus of a user equipment (UE), comprising: receiving informationidentifying a timing offset associated with uplink (UL) and downlink(DL) communications of the apparatus of the UE; and determining a targetbase station timing advance value for a handover to a target basestation based on at least one of the information identifying the timingoffset, a timing difference between the target base station and a sourcebase station associated with the UE, or a source base station timingadvance value associated with the source base station.
 2. The method ofclaim 1, further comprising: determining the timing difference betweenthe target base station and the source base station based at least inpart on reference signaling received from the source base station andthe target base station.
 3. The method of claim 1, wherein the timingoffset is based at least in part on a switching time, a propagationdelay between transmit and reception, or a hardware configuration of atleast one of the UE, the source base station, or the target basestation.
 4. The method of claim 1, wherein a granularity of the timingoffset is based at least in part on at least one of a numerology, or aslot length of the target base station.
 5. The method of claim 1,wherein the information identifying the timing offset is received in ahandover command.
 6. The method of claim 1, wherein the target basestation timing advance value is determined without performing a randomaccess procedure.
 7. The method of claim 1, wherein the target basestation timing advance value is determined based at least in part on theinformation identifying the timing offset, the timing difference betweenthe target base station and the source base station, and the source basestation timing advance value.
 8. A method of wireless communicationperformed by an apparatus of a user equipment (UE), comprising:transmitting at least one of: information identifying a timingdifference between a target base station and a source base stationassociated with a handover, or an uplink reference signal; and receivinginformation identifying a target base station timing advance value,wherein the information identifying the target base station timingadvance value is based at least in part on the timing difference betweenthe target base station and the source base station or the uplinkreference signal.
 9. The method of claim 8, wherein the handover isperformed without performing a random access procedure.
 10. The methodof claim 8, wherein the information identifying the timing differencebetween the target base station and the source base station is aquantization of the timing difference between the target base stationand the source base station.
 11. The method of claim 8, wherein theinformation identifying the timing difference between the target basestation and the source base station is provided in a radio resourcemanagement report.
 12. The method of claim 8, wherein the uplinkreference signal comprises a sounding reference signal.
 13. A method ofwireless communication performed by an apparatus of a target basestation, comprising: receiving, from a user equipment (UE), at least oneof: information identifying a timing difference between the apparatus ofthe target base station and a source base station, wherein the apparatusof the target base station and the source base station are associatedwith a handover of the UE, or an uplink reference signal; and providing,to the UE, information identifying a target base station timing advancevalue, wherein the target base station timing advance value is based atleast in part on the information identifying the timing difference orthe uplink reference signal.
 14. The method of claim 13, wherein theinformation identifying the timing difference between the apparatus ofthe target base station and the source base station is a quantization ofthe timing difference between the apparatus of the target base stationand a source base station.
 15. The method of claim 13, wherein theinformation identifying the timing difference between the apparatus ofthe target base station and the source base station is received in aradio resource management report.
 16. The method of claim 13, whereinthe uplink reference signal comprises a sounding reference signal. 17.The method of claim 13, further comprising: determining the target basestation timing advance value based at least in part on the informationidentifying the timing difference between the apparatus of the targetbase station and the source base station or the uplink reference signal.18. The method of claim 13, further comprising: selecting a techniquefor determining the target base station timing advance value based atleast in part on the information identifying the timing differencebetween the apparatus of the target base station and the source basestation or the uplink reference signal.
 19. The method of claim 18,wherein the technique is selected from a plurality of techniquesincluding at least one of: determining the target base station timingadvance value as zero, determining the target base station timingadvance value in accordance with a source base station timing advancevalue associated with the source base station, or determining the targetbase station timing advance value using the uplink reference signal. 20.The method of claim 13, wherein providing, to the UE, informationidentifying the target base station timing advance value furthercomprises: providing, to the source base station to be transmitted tothe UE, the information identifying the target base station timingadvance value.